According to the 3'rd generation partnership project (3GPP) technical specification, 3G TS 23.060 v3.4.0 (2000-07) a common packet domain Core Network is used for both GSM and UMTS. Such a system has been shown in FIG. 1. A similar system has been shown in WO99/05828.
The above Core Network provides packet-switched (PS) services and is designed to support several quality of services levels in order to allow efficient transfer of non real-time traffic (e.g., intermittent and bursty data transfers, occasional transmission of large volumes of data) and real-time traffic (e.g., voice, video). One class of quality of service pertains to a low throughput and a low delay; another class pertains to higher throughput and longer delay and a further class pertains to relatively long delays and high throughput.
Applications based on standard data protocols and SMS are supported, and interworking is defined with IP networks. Charging is rendered flexible and allows Internet Service Providers to bill according to the amount of data transferred, the QoS supported, and the duration of the connection.
Each PLMN has two access points, the radio interface (labelled Um in GSM and Uu in UMTS) used for mobile access and the R reference point used for origination or reception of messages.
An interface differs from a reference point in that an interface is defined where specific information is exchanged and needs to be fully recognised. There is an inter PLMN interface called Gp that connects two independent packet domain networks for message exchange. There is also a PLMN to fixed network (typically a packet data network) reference point called Gi.
There may be more than a single network interface to several different packet data (or other) networks. These networks may both differ in ownership as well as in communications protocol (e.g., TCP/IP etc.). The network operator should define and negotiate interconnect with each external (PDN or other) network.
Network interworking is required whenever a packet domain PLMN and any other network are involved in the execution of a service request. With reference to FIG. 1, interworking takes place through the Gi reference point and the Gp interface.
The internal mechanism for conveying the PDP (Packet Data Protocol) PDU (Packet Data Unit) through the PLMN is managed by the PLMN network operator and is not apparent to the data user. The use of the packet domain data service may have an impact on and increase the transfer time normally found for a message when communicated through a fixed packet data network.
The packet domain supports interworking with networks based on the Internet protocol (IP). The packet domain may provide compression of the TCP/IP header when an IP datagram is used within the context of a TCP connection.
The packet domain PLMN service is an IP domain, and mobile terminals offered service by a service provider may be globally addressable through the network operator's addressing scheme.
A GPRS Support Node (GSN) contains functionality required to support GPRS functionality for GSM and/or UMTS. In one PLMN, there may be more than one GSN.
The Gateway GPRS Support Node (GGSN) is the node that is accessed by the packet data network due to evaluation of the PDP address. It contains routing information for PS-attached users. The routing information is used to tunnel N-PDUs to the MS's current point of attachment, i.e., the Serving GPRS Support Node. The GGSN may request location information from the HLR via the optional Gc interface. The GGSN is the first point of PDN interconnection with a GSM PLMN supporting GPRS (i.e., the Gi reference point is supported by the GGSN). GGSN functionality is common for GSM and UMTS.
The Serving GPRS Support Node (SGSN) is the node that is serving the MS. The SGSN supports GPRS for GSM (i.e., the Gb interface is supported by the SGSN) and/or UMTS (i.e., the lu interface is supported by the SGSN).
In order to access the PS services, an MS shall first make its presence known to the network by performing a GPRS Attach. This makes the MS available for SMS over PS, paging via the SGSN, and notification of incoming PS data. According to the Attach, the IMSI (International Mobile Subscription Identity) of the mobile station (MS) is mapped to one or more packet data protocol addresses (PDP).
At PS Attach, the SGSN establishes a mobility management context containing information pertaining to e.g., mobility and security for the MS.
In order to send and receive PS data, the MS shall activate the Packet Data Protocol context that it wants to use. This operation makes the MS known in the corresponding GGSN, and interworking with external data networks can commence.
At PDP Context Activation, the SGSN establishes a PDP context, to be used for routing purposes, with the GGSN that the subscriber will be using.
The SGSN and GGSN functionalities may be combined in the same physical node, or they may reside in different physical nodes. SGSN and GGSN contain IP or other (operator's selection, e.g., ATM-SVC) routing functionality, and they may be interconnected with IP routers. In UMTS, the SGSN and RNC may be interconnected with one or more IP routers. When SGSN and GGSN are in different PLMNs, they are interconnected via the Gp interface. The Gp interface provides the functionality of the Gn interface, plus security functionality required for inter-PLMN communication. The security functionality is based on mutual agreements between operators.
The SGSN may send location information to the MSC/VLR via the optional Gs interface. The SGSN may receive paging requests from the MSC/VLR via the Gs interface.
According to the PDP context activation, a network bearer (IP) communication between the mobile station and the Internet service provider (ISP) is established. Moreover, a given class of Quality of Service class is assigned for the communication to be performed.
The Charging Gateway Functionality (CGF) collects charging records from SGSNs and GGSNs. The HLR (Home Location Register) contains GSM and UMTS subscriber information. The HLR stores the IMSI (International Mobile Subscription Identity) and maps the IMSI to one or more packet data protocol addresses (PDP) and maps each PDP address to one or more GGSN's.
The SMS-GMSCs and SMS-IWMSCs support SMS transmission via the SGSN. Optionally, the MSC/VLR can be enhanced for more-efficient co-ordination of packet-switched and circuit-switched services and functionality: e.g., combined GPRS and non-GPRS location updates.
User data is transferred transparently between the MS and the external data networks with a method known as encapsulation and tunnelling: data packets are equipped with PS-specific protocol information and transferred between the MS and the GGSN. This transparent transfer method lessens the requirement for the PLMN to interpret external data protocols, and it enables easy introduction of additional interworking protocols in the future.
An Application Server (AS) is connected to the Packet Data Network (PDN) for providing information. The application server may be owned by an Internet Service Provider (ISP), the PLMN, or an independent company.
MS Initiated PDP Context Activation
We shall now revert to the PDP context activation procedure.
In FIG. 2, a sequence diagram relating to the Mobile Station initiated context activation procedure has been shown.                1) The MS sends an Activate PDP Context Request (NSAPI, TI, PDP Type, PDP Address, Access Point Name, QoS Requested, PDP Configuration Options) message to the SGSN. The MS may use Access Point Name to select a reference point to a certain external network and/or to select a service. QoS Requested indicates the desired QoS profile.        3) In UMTS, RAB (Radio Bearer) set-up is done by the RAB Assignment procedure.        4) If BSS trace is activated, then the SGSN shall send an Invoke Trace (Trace Reference, Trace Type, Trigger Id) message to the BSS or UTRAN. Trace Reference and Trace Type are copied from the trace information received from the HLR. Thereby, the location of the mobile station can be established.        5a) The SGSN validates the Activate PDP Context Request using PDP Type (optional), PDP Address (optional), and Access Point Name (optional) provided by the MS and the PDP context subscription records                    The SGSN may restrict the requested QoS attributes given its capabilities, the current load, and the subscribed QoS profile.            The SGSN sends a Create PDP Context Request (PDP Type, PDP Address, Access Point Name, QoS Negotiated, TEID, NSAPI, MSISDN, Selection Mode, Charging Characteristics, Trace Reference, Trace Type, Trigger Id, PDP Configuration Options) message to the affected GGSN                        5b) The GGSN creates a new entry in its PDP context table and generates a Charging Id. The new entry allows the GGSN to route PDP PDUs between the SGSN and the external PDP network, and to start charging. The GGSN then returns a Create PDP Context Response (TEID, PDP Address, PDP Configuration Options, QoS Negotiated, Charging Id, Cause) message to the SGSN.        6) The SGSN selects Radio Priority and Packet Flow Id based on QoS Negotiated, and returns an Activate PDP Context Accept (PDP Type, PDP Address, TI, QoS Negotiated, Radio Priority, Packet Flow Id, PDP Configuration Options) message to the MS. The SGSN is now able to route PDP PDUs between the GGSN and the MS, and to start charging.        7) Now, a packet data session is open between the Mobile Station (MS) and the Application Server (AS).        
For each PDP Address, a different quality of service (QoS) profile may be requested. For example, some PDP addresses may be associated with E-mail that can tolerate lengthy response times. Other applications cannot tolerate delay and demand a very high level of throughput, interactive applications being one example. These different requirements are reflected in the QoS profile. If a QoS profile requirement is beyond the capabilities of a PLMN, the PLMN negotiates the QoS profile as close as possible to the requested QoS profile. The MS either accepts the negotiated QoS profile, or deactivates the PDP context.
AS Initiated PDP Context Activation
The scenario for setting up a session initiated by the an external application server has been illustrated by the sequence diagram shown in FIG. 3:
The Network-Requested PDP Context Activation procedure allows the GGSN to initiate the activation of a PDP context. When receiving a PDP PDU the GGSN checks if a PDP context is established for that PDP address. If no PDP context has been previously established the GGSN may try to deliver the PDP PDU by initiating the Network-Requested PDP Context Activation procedure.                1) When receiving a PDP PDU the GGSN determines if the Network-Requested PDP Context Activation procedure has to be initiated. The GGSN may store subsequent PDP PDU's received for the same PDP address.        2a) The GGSN may send a Send Routing Information for GPRS (IMSI) message to the HLR.        2b) If the HLR determines that the request can be served, it returns a Send Routing Information for GPRS Ack (IMSI, SGSN Address, Mobile Station Not Reachable Reason) message to the GGSN.        3a) The GGSN shall send a PDU Notification Request (IMSI, PDP Type, PDP Address, APN) message to the SGSN indicated by the HLR.        3b)The SGSN returns a PDU Notification Response (Cause) message to the GGSN in order to acknowledge that it shall request the MS to activate the PDP context indicated with PDP Address.        4) The SGSN sends a Request PDP Context Activation (TI, PDP Type, PDP Address, APN) message to request the MS to activate the indicated PDP context.        5) The PDP context is activated with the PDP Context Activation procedure.        
As mentioned above, it is possible that the mobile station needs a different QoS from what was initially needed. In order to modify the QoS, the mobile station may take one of the following steps:                The MS initiates a new primary PDP Context.        There is an active PDP context, but it is established with insufficient bandwidth, QoS. The MS may trigger a PDP Context Modification.        There is an active PDP context, but it is established with insufficient bandwidth, QoS. The MS may trigger a secondary PDP Context Modification.        
The two latter procedures shall be dealt with below.
In FIG. 4, a procedure of the mobile station modifying the PDP context is shown in which the following steps are carried out:                1) The MS sends a Modify PDP Context Request (TI, QoS Requested, TFT) message to the SGSN. Either QoS Requested or TFT or both may be included. QoS Requested indicates the desired QoS profile, while TFT indicates the TFT that is to be added or modified or deleted from the PDP context.        2) The SGSN may restrict the desired QoS profile given its capabilities, the current load, and the subscribed QoS profile. The SGSN sends an Update PDP Context Request (TEID, NSAPI, QoS Negotiated, TFT) message to the GGSN. If QoS Negotiated and/or TFT received from the SGSN is incompatible with the PDP context being modified (e.g., TFT contains inconsistent packet filters), then the GGSN rejects the Update PDP Context Request. The compatible QoS profiles are configured by the GGSN operator.        3) The GGSN may further restrict QoS Negotiated given its capabilities and the current load. The GGSN stores QoS Negotiated, stores, modifies, or deletes TFT of that PDP context as indicated in TFT, and returns an Update PDP Context Response (TEID, QoS Negotiated) message.        4) In UMTS, radio access bearer modification may be performed by the RAB Assignment procedure.        5) The SGSN selects Radio Priority and Packet Flow Id based on QoS Negotiated, and returns a Modify PDP Context Accept (TI, QoS Negotiated, Radio Priority, Packet Flow Id) message to the MS.        
In FIG. 5, a procedure for activation of a secondary PDP context has been shown in which the following steps are carried out:                1) The MS sends an Activate Secondary PDP Context Request (Linked TI, NSAPI, TI, QoS Requested, TFT) message to the SGSN. Linked TI indicates the TI value assigned to any one of the already activated PDP contexts for this PDP address and APN. QoS Requested indicates the desired QoS profile. TFT is sent transparently through the SGSN to the GGSN to enable packet classification for downlink data transfer. TI and NSAPI contain values not used by any other activated PDP context.        2) In GSM, security functions may be executed.        3) In UMTS, RAB set-up is done by the RAB Assignment procedure.        4a) The SGSN validates the Activate Secondary PDP Context Request using the TI indicated by Linked TI. The same GGSN address is used by the SGSN as for the already-activated PDP context(s) for that TI and PDP address.                    The SGSN and GGSN may restrict and negotiate the requested QoS. The SGSN sends a Create PDP Context Request (QoS Negotiated, TEID, NSAPI, Primary NSAPI, TFT) message to the affected GGSN. Primary NSAPI indicates the NSAPI value assigned to any one of the already activated PDP contexts for this PDP address and APN. TFT is included only if received in the Activate Secondary PDP Context Request message. The GGSN uses the same external network as used by the already-activated PDP context(s) for that PDP address, generates a new entry in its PDP context table, and stores the TFT. The new entry allows the GGSN to route PDP PDUs via different GTP tunnels between the SGSN and the external PDP network.                        4b) The GGSN returns a Create PDP Context Response (TEID, QoS Negotiated, Cause) message to the SGSN.        
In GSM, BSS packet flow context procedures may be executed.                5) The SGSN selects Radio Priority and Packet Flow Id based on QoS Negotiated, and returns an Activate Secondary PDP Context Accept (TI, QoS Negotiated, Radio Priority, Packet Flow Id) message to the MS. The SGSN is now able to route PDP PDUs between the GGSN and the MS via different GTP tunnels and possibly different LLC links.Push Services        
One type of service which can be accomplished in the above system is so-called “push” services, that is, an Application Server (AS) takes the initiative to render information, such as stock quotes, news or commercials, available to one or a plurality of mobile terminals.